The poem begins with a memory of crawling like spiderlings, small and hopeful, back when the speaker and a "you" were somehow already headed toward dust. While the other person watched a sunset, the speaker watched darkness creep up the trees, which suggests a mind drawn to what is ending rather than what is glowing. The speaker then describes a hump, grown "as a form of protest," that now looms invisibly over every croak and cry. The humor is dry, but the weight is real: it reads like a bent-over, aging, or burdened way of living.
The speaker names this hump "O," for Oblivion and the Obvious, treating death as both a dread and a plain fact. The turn comes near the end. What looked like living spiderlings turns out to be the leftover shell of their eggs. The closing lines admit that in the right light, anything can look promising, including the two people themselves. The mood is wry, quiet, and disillusioned, with a little tenderness left over.